Subtree of Another Tree.js

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @param {TreeNode} subRoot
 * @return {boolean}
 */
var isSubtree = function(root, subRoot) {
	if(subRoot === null)  return true;
	if(root === null) return false;

	if (isSameTree(root, subRoot)) {
		return true;
	}

	return (isSubtree(root.left, subRoot) || isSubtree(root.right, subRoot));
};

function isSameTree(root, subRoot) {
	if(root === null && subRoot === null) {
	   return true;
	}

	if((root && subRoot === null) || (root === null && subRoot)) {
		return false;
	} 

	if(root.val !== subRoot.val) {
		return false;
	}
	return (isSameTree(root.left, subRoot.left) && isSameTree(root.right, subRoot.right));
}